Radical oxidation process for fabricating a nonvolatile charge trap memory device

ABSTRACT

A method for fabricating a nonvolatile charge trap memory device is described. The method includes subjecting a substrate to a first oxidation process to form a tunnel oxide layer overlying a polysilicon channel, and forming over the tunnel oxide layer a multi-layer charge storing layer comprising an oxygen-rich, first layer comprising a nitride, and an oxygen-lean, second layer comprising a nitride on the first layer. The substrate is then subjected to a second oxidation process to consume a portion of the second layer and form a high-temperature-oxide (HTO) layer overlying the multi-layer charge storing layer. The stoichiometric composition of the first layer results in it being substantially trap free, and the stoichiometric composition of the second layer results in it being trap dense. The second oxidation process can comprise a plasma oxidation process or a radical oxidation process using In-Situ Steam Generation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S.application Ser. No. 12/197,466, filed Aug. 25, 2008, which is acontinuation of U.S. application Ser. No. 12/124,855, filed May 21,2008, which claims the benefit of priority under 35 U.S.C. 119(e) toU.S. Provisional Patent Application Ser. No. 60/940,139, filed May 25,2007, and U.S. Provisional Application No. 60/986,637, filed Nov. 9,2007, all of which are incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the present invention are in the field of SemiconductorFabrication and, in particular, Semiconductor Device Fabrication.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,lending to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

Non-volatile semiconductor memories typically use stacked floating gatetype field-effect-transistors. In such transistors, electrons areinjected into a floating gate of a memory cell to be programmed bybiasing a control gate and grounding a body region of a substrate onwhich the memory cell is formed. An oxide-nitride-oxide (ONO) stack isused as either a charge storing layer, as in asemiconductor-oxide-nitride-oxide-semiconductor (SONOS) transistor, oras an isolation layer between the floating gate and control gate, as ina split gate flash transistor. FIG. 1 illustrates a cross-sectional viewof a conventional nonvolatile charge trap memory device.

Referring to FIG. 1, semiconductor device 100 includes a SONOS gatestack 104 including a conventional ONO portion 106 formed over a siliconsubstrate 102. Semiconductor device 100 further includes source anddrain regions 110 on either side of SONOS gate stack 104 to define achannel region 112. SONOS gate stack 104 includes a poly-silicon gatelayer 108 formed above and in contact with ONO portion 106. Polysilicongate layer 108 is electrically isolated from silicon substrate 102 byONO portion 106. ONO portion 106 typically includes a tunnel oxide layer1 06A, a nitride or oxynitride charge-trapping layer 106B, and a topoxide layer 106C overlying nitride or oxynitride layer 106B.

One problem with conventional SONOS transistors is the poor dataretention in the nitride or oxy-nitride layer 106B that limitssemiconductor device 100 lifetime and its use in several applicationsdue to leakage current through the layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not limitation, in the figures of the accompanying drawings inwhich:

FIG. 1 illustrates a cross-sectional view of a conventional nonvolatilecharge trap memory device.

FIG. 2 illustrates a cross-sectional view of an oxidation chamber of abatch-processing tool, in accordance with an embodiment of the presentinvention.

FIG. 3 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 4A illustrates a cross-sectional view of a substrate having acharge trapping layer formed thereon, corresponding to operation 302from the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention.

FIG. 4B illustrates a cross-sectional view of a substrate having acharge trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 304 from the Flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 5 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 6A illustrates a cross-sectional view of a substrate, correspondingto operation 502 from the Flowchart of FIG. 5, in accordance with anembodiment of the present invention.

FIG. 6B illustrates a cross-sectional view of a substrate having a firstdielectric layer formed thereon, corresponding to operation 504 from theFlowchart of FIG. 5, in accordance with an embodiment of the presentinvention.

FIG. 6C illustrates a cross-sectional view of a substrate having acharge trapping layer formed thereon, corresponding to operation 508from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention.

FIG. 6D illustrates a cross-sectional view of a substrate having acharge trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 510 from the Flowchart of FIG. 5, inaccordance with an embodiment of the present invention.

FIG. 6E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 7 A illustrates a cross-sectional view of a substrate includingfirst and second exposed crystal planes, in accordance with anembodiment of the present invention.

FIG. 7B illustrates a cross-sectional view of the substrate includingfirst and second crystal planes and having a dielectric layer formedthereon, in accordance with an embodiment of the present invention.

FIG. 8 illustrates an arrangement of process chambers in a cluster tool,in accordance with an embodiment of the present invention.

FIG. 9 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 10A illustrates a cross-sectional view of a substrate, inaccordance with an embodiment of the present invention.

FIG. 10B illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 402from the Flowchart of FIG. 4, in accordance with an embodiment of thepresent invention.

FIG. 10C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 406from the Flowchart of FIG. 4, in accordance with an embodiment of thepresent invention.

FIG. 10D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 408 from theFlowchart of FIG. 4, in accordance with an embodiment of the presentinvention.

FIG. 10E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 11 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 12A illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 602from the Flowchart of FIG. 6, in accordance with an embodiment of thepresent invention.

FIG. 12B illustrates a cross-sectional view of a substrate having anoxygen-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 606 from the Flowchart ofFIG. 6, in accordance with an embodiment of the present invention.

FIG. 12C illustrates a cross-sectional view of a substrate having asilicon-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 610 from the Flowchart ofFIG. 6, in accordance with an embodiment of the present invention.

FIG. 12D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 612 from theFlowchart of FIG. 6, in accordance with an embodiment of the presentinvention.

FIG. 12E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 13A illustrates a cross-sectional view of a substrate includingfirst and second exposed crystal planes, in accordance with anembodiment of the present invention.

FIG. 13B illustrates a cross-sectional view of the substrate includingfirst and second crystal planes and having a dielectric layer formedthereon, in accordance with an embodiment of the present invention.

FIG. 14 illustrates a cross-sectional view of a nonvolatile charge trapmemory device including an ONONO stack.

FIG. 15 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device includingan ONONO stack, in accordance with an embodiment of the presentinvention.

FIG. 16A illustrates a non-planar multigate device including a splitcharge-trapping region.

FIG. 16B illustrates a cross-sectional view of the non-planar multigatedevice of FIG. 16A.

FIGS. 17A and 17B illustrate a non-planar multigate device including asplit charge-trapping region and a horizontal nanowire channel.

FIG. 17C illustrates a cross-sectional view of a vertical string ofnon-planar multigate devices of FIG. 17A.

FIGS. 18A and 18B illustrate a non-planar multigate device including asplit charge-trapping region and a vertical nanowire channel.

FIG. 19A through 19F illustrate a gate first scheme for fabricating thenon-planar multigate device of FIG. 18A.

FIG. 20A through 20F illustrate a gate last scheme for fabricating thenon-planar multigate device of FIG. 18A.

DETAILED DESCRIPTION

Embodiments of a non-volatile charge trap memory device integrated withlogic devices are described herein with reference to figures. However,particular embodiments may be practiced without one or more of thesespecific details, or in combination with other known methods, materials,and apparatuses. In the following description, numerous specific detailsare set forth, such as specific materials, dimensions and processesparameters etc. to provide a thorough understanding of the presentinvention. In other instances, well-known semiconductor design andfabrication techniques have not been described in particular detail toavoid unnecessarily obscuring the present invention. Referencethroughout this specification to “an embodiment” means that a particularfeature, structure, material, or characteristic described in connectionwith the embodiment is included in at least one embodiment of theinvention. Thus, the appearances of the phrase “in an embodiment” invarious places throughout this specification are not necessarilyreferring to the same embodiment of the invention. Furthermore, theparticular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments.

Methods to fabricate a nonvolatile charge trap memory device aredescribed herein. In the following description, numerous specificdetails are set forth, such as specific dimensions, in order to providea thorough understanding of the present invention. It will be apparentto one skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownprocessing steps, such as patterning steps or wet chemical cleans, arenot described in detail in order to not unnecessarily obscure thepresent invention. Furthermore, it is to be understood that the variousembodiments shown in the Figures are illustrative representations andare not necessarily drawn to scale.

Disclosed herein is a method to fabricate a nonvolatile charge trapmemory device. A substrate may first be provided having acharge-trapping layer disposed thereon. In one embodiment, a portion ofthe charge-trapping layer is then oxidized to form a blocking dielectriclayer above the charge-trapping layer by exposing the charge-trappinglayer to a radical oxidation process.

Formation of a dielectric layer by a radical oxidation process mayprovide higher quality films than processes involving steam growth, i.e.wet growth processes. Furthermore, a radical oxidation process carriedout in a batch-processing chamber may provide high quality films withoutimpacting the throughput (wafers/Hr) requirements that a fabricationfacility may require. By carrying out the radical oxidation process attemperatures compatible with such a chamber, such as temperaturesapproximately in the range of 600-900 degrees Celsius, the thermalbudget tolerated by the substrate and any other features on thesubstrate may not be impacted to the extent typical of processes over1000 degrees Celsius. In accordance with an embodiment of the presentinvention, a radical oxidation process involving flowing hydrogen (H2)and oxygen (02) gas into a batch-processing chamber is carried out toeffect growth of a dielectric layer by oxidation consumption of anexposed substrate or film. In one embodiment, multiple radical oxidationprocesses are carried out to provide a tunnel dielectric layer and ablocking dielectric layer for a non-volatile charge trap memory device.These dielectric layers may be of very high quality, even at a reducedthickness. In one embodiment, the tunnel dielectric layer and theblocking dielectric layer are both denser and are composed ofsubstantially fewer hydrogen atoms/cm3 than a tunnel dielectric layer ora blocking dielectric layer formed by wet oxidation techniques. Inaccordance with another embodiment of the present invention, adielectric layer formed by carrying out a radical oxidation process isless susceptible to crystal plane orientation differences in thesubstrate from which it is grown. In one embodiment, the corneringeffect caused by differential crystal plane oxidation rates issignificantly reduced by forming a dielectric layer via a radicaloxidation process.

A portion of a nonvolatile charge trap memory device may be fabricatedby carrying out a radical oxidation process in a process chamber. Inaccordance with an embodiment of the present invention, the processchamber is a batch-processing chamber. FIG. 2 illustrates across-sectional view of an oxidation chamber of a batch-processing tool,in accordance with that embodiment. Referring to FIG. 2, abatch-processing chamber 200 includes a carrier apparatus 204 to hold aplurality of semiconductor wafers 202. In one embodiment, thebatch-processing chamber is an oxidation chamber. In a specificembodiment, the process chamber is a low-pressure chemical vapordeposition chamber. The plurality of semiconductor wafers 202 may bearranged in such a way as to maximize exposure of each wafer to aradical oxidation process, while enabling the inclusion of a reasonablenumber of wafers (e.g. 25 wafers), to be processed in a single pass. Itshould be understood, however, that the present invention is not limitedto a batch-processing chamber.

In an aspect of the present invention, a portion of a nonvolatile chargetrap memory device is fabricated by a radical oxidation process. FIG. 3depicts a Flowchart representing a series of operations in a method forfabricating a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention. FIGS. 4A-4B illustratecross-sectional views representing operations in the fabrication of anonvolatile charge trap memory device, in accordance with an embodimentof the present invention.

FIG. 4A illustrates a cross-sectional view of a substrate having acharge trapping layer formed thereon, corresponding to operation 302from the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention. Referring to operation 302 of Flowchart 300 andcorresponding FIG. 4A, a substrate 400 is provided having acharge-trapping layer disposed thereon. In an embodiment, thecharge-trapping layer has a first region 404A and a second region 404Bdisposed above substrate 400. In one embodiment, a dielectric layer 402is disposed between substrate 400 and the charge trapping layer, asdepicted in FIG. 4A. The charge-trapping layer may be composed of amaterial and have a thickness suitable to store charge and, hence,change the threshold voltage of a subsequently formed gate stack. In anembodiment, region 404A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 404B of the as-formed chargetrapping layer will be consumed to form a second dielectric layer, aboveregion 404A.

FIG. 4B illustrates a cross-sectional view of a substrate having acharge trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 304 from the Flowchart of FIG. 3, inaccordance with an embodiment of the present invention. Referring tooperation 304 of Flowchart 300 and corresponding FIG. 4B, a blockingdielectric layer 406 is formed on charge-trapping layer 404. Inaccordance with an embodiment of the present invention, blockingdielectric layer 406 is formed by oxidizing region 404B of thecharge-trapping layer by exposing the charge-trapping layer to a radicaloxidation process. In that embodiment, region 404A of the originalcharge trapping layer is now labeled as charge-trapping layer 404.

Blocking dielectric layer 406 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. In a specificembodiment, region 404B is a silicon-rich silicon oxy-nitride regionhaving a thickness approximately in the range of 2-3 nanometers and isoxidized to form blocking dielectric layer 406 having a thicknessapproximately in the range of 3.5-4.5 nanometers. In that embodiment,blocking dielectric layer 406 is composed of silicon dioxide.

Blocking dielectric layer 406 may be formed by a radical oxidationprocess. In accordance with an embodiment of the present invention, theradical oxidation process involves flowing hydrogen (Hz) and oxygen (Oz)gas into a furnace, such as the batch processing chamber 200 describedin association with FIG. 2. In one embodiment, the partial pressures ofHz and Oz have a ratio to one another of approximately 1:1. However, inan embodiment, an ignition event is not carried out which wouldotherwise typically be used to pyrolyze the H₂ and O₂ to form steam.Instead, H₂ and O₂ are permitted to react to form radicals at thesurface of region 404B. In one embodiment, the radicals are used toconsume region 404B to provide blocking dielectric layer 406. In aspecific embodiment, the radical oxidation process includes oxidizingwith a radical such as, but not limited to, an OH radical, an H0₂radical or an O diradical at a temperature approximately in the range of600-900 degrees Celsius. In a particular embodiment, the radicaloxidation process is carried out at a temperature approximately in therange of 700-800 degrees Celsius at a pressure approximately in therange of 0.5-5 Torr. In one embodiment, the second radical oxidationprocess is carried out for a duration approximately in the range of100-150 minutes.

Referring to operation 306 of Flowchart 300, blocking dielectric layer406 may be further subjected to a nitridation process in the firstprocess chamber. In accordance with an embodiment of the presentinvention, the nitridation process includes annealing blockingdielectric layer 406 in an atmosphere including nitrogen at atemperature approximately in the range of 700-800 degrees Celsius for aduration approximately in the range of 5 minutes-60 minutes. In oneembodiment, the atmosphere including nitrogen is composed of a gas suchas, but not limited to, nitrogen (N2), nitrous oxide (N20), nitrogendioxide (N02), nitric oxide (NO) or ammonia (NH3). Alternatively, thisnitridation step, i.e. operation 306 from Flowchart 300, may be skipped.

In an aspect of the present invention, both a tunnel dielectric layerand a blocking dielectric layer may be formed by radical oxidationprocesses. FIG. 5 depicts a Flowchart 500 representing a series ofoperations in a method for fabricating a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention. FIGS.6A-6E illustrates cross-sectional views representing operations in thefabrication of a nonvolatile charge trap memory device, in accordancewith an embodiment of the present invention.

FIG. 6A illustrates a cross-sectional view of a substrate, correspondingto operation 502 from the Flowchart of FIG. 5, in accordance with anembodiment of the present invention. Referring to operation 502 ofFlowchart 500 and corresponding FIG. 6A, a substrate 600 is provided ina process chamber.

Substrate 600 may be composed of a material suitable for semiconductordevice fabrication. In one embodiment, substrate 600 is a bulk substratecomposed of a single crystal of a material which may include, but is notlimited to, silicon, germanium, silicon-germanium or a III-V compoundsemiconductor material. In another embodiment, substrate 600 includes abulk layer with a top epitaxial layer. In a specific embodiment, thebulk layer is composed of a single crystal of a material which mayinclude, but is not limited to, silicon, germanium, silicon-germanium, aIII-V compound semiconductor material or quartz, while the top epitaxiallayer is composed of a single crystal layer which may include, but isnot limited to, silicon, germanium, silicon-germanium or a III-Vcompound semiconductor material. In another embodiment, substrate 600includes a top epitaxial layer on a middle insulator layer which isabove a lower bulk layer. The top epitaxial layer is composed of asingle crystal layer which may include, but is not limited to, silicon(i.e. to form a silicon-on-insulator (SOl) semiconductor substrate),germanium, silicon-germanium or a III-V compound semiconductor material.The insulator layer is composed of a material which may include, but isnot limited to, silicon dioxide, silicon nitride or silicon oxy-nitride.The lower bulk layer is composed of a single crystal which may include,but is not limited to, silicon, germanium, silicon-germanium, a III-Vcompound semiconductor material or quartz. Substrate 600 may furtherinclude dopant impurity atoms.

FIG. 6B illustrates a cross-sectional view of a substrate having adielectric layer formed thereon, corresponding to operation 504 from theFlowchart of FIG. 5, in accordance with an embodiment of the presentinvention. Referring to operation 504 of Flowchart 500 and correspondingFIG. 6B, substrate 600 is subjected to a first radical oxidation processto form a first dielectric layer 602.

First dielectric layer 602 may be composed of a material and have athickness suitable to allow charge carriers to tunnel into asubsequently formed charge trapping layer under an applied gate bias,while maintaining a suitable barrier to leakage when a subsequentlyformed nonvolatile charge trap memory device is unbiased. Firstdielectric layer 602 may be referred to in the art as a tunneldielectric layer. In accordance with an embodiment of the presentinvention, first dielectric layer 602 is formed by an oxidation processwhere the top surface of substrate 600 is consumed. Thus, in anembodiment, first dielectric layer 602 is composed of an oxide of thematerial of substrate 600. For example, in one embodiment, substrate 600is composed of silicon and first dielectric layer 602 is composed ofsilicon dioxide. In a specific embodiment, first dielectric layer 602 isformed to a thickness approximately in the range of 1-10 nanometers. Ina particular embodiment, first dielectric layer 602 is formed to athickness approximately in the range of 1.5-2.5 nanometers.

First dielectric layer 602 may be formed by a radical oxidation process.In accordance with an embodiment of the present invention, the radicaloxidation process involves flowing hydrogen (H2) and oxygen (02) gasinto a furnace, such as the batch processing chamber 200 described inassociation with FIG. 2. In one embodiment, the partial pressures of Hzand Oz have a ratio to one another of approximately 1:1. However, in anembodiment, an ignition event is not carried out which would otherwisetypically be used to pyrolyze the Hz and Oz to form steam. Instead, Hzand Oz are permitted to react to form radicals at the surface ofsubstrate 600. In one embodiment, the radicals are used to consume thetop portion of substrate 600 to provide first dielectric layer 602. In aspecific embodiment, the radical oxidation process includes oxidizingwith a radical such as, but not limited to, an OH radical, an HO₂radical or an 0 diradical at a temperature approximately in the range of600-900 degrees Celsius. In a particular embodiment, the radicaloxidation process is carried out at a temperature approximately in therange of 700-800 degrees Celsius at a pressure approximately in therange of 0.5-5 Torr. In one embodiment, the radical oxidation process iscarried out for a duration approximately in the range of 100-150minutes. In accordance with an embodiment of the present invention,first dielectric layer 602 is formed as a high-density,low-hydrogen-content film.

Referring to operation 506 of Flowchart 500, subsequent to forming firstdielectric layer 602, but prior to any further processing, firstdielectric layer 602 may be subjected to a nitridation process. In anembodiment, the nitridation process is carried out in the same processchamber used to form first dielectric layer 502, without removingsubstrate 600 from the process chamber between process steps. In oneembodiment, the annealing includes heating substrate 600 in anatmosphere including nitrogen at a temperature approximately in therange of 700-800 degrees Celsius for a duration approximately in therange of 5 minutes-60 minutes. In one embodiment, the atmosphereincluding nitrogen is composed of a gas such as, but not limited to,nitrogen (N₂), nitrous oxide (N₂O), nitrogen dioxide (NO₂), nitric oxide(NO) or ammonia (NH₃). In one embodiment, the nitridation occursfollowing a nitrogen or argon purge of the process chamber following thefirst radical oxidation process. Alternatively, the above nitridationstep may be skipped.

FIG. 6C illustrates a cross-sectional view of a substrate having acharge trapping layer formed thereon, corresponding to operation 508from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention. Referring to operation 508 of Flowchart 500 andcorresponding FIG. 6C, a charge-trapping layer having a first region604A and a second region 604B is formed on first dielectric layer 602.In an embodiment, the formation of the charge-trapping layer is carriedout in the same process chamber used to form first dielectric layer 602,without removing substrate 600 from the process chamber between processsteps.

The charge-trapping layer may be composed of a material and have athickness suitable to store charge and, hence, change the thresholdvoltage of a subsequently formed gate stack. In accordance with anembodiment of the present invention, the charge-trapping layer iscomposed of two regions 604A and 604B, as depicted in FIG. 6C. In anembodiment, region 604A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 604B of the as-formedcharge-trapping layer will be consumed to form a second dielectriclayer, above region 604A.

The charge-trapping layer having regions 604A and 604B may be formed bya chemical vapor deposition process. In accordance with an embodiment ofthe present invention, the charge-trapping layer is composed of amaterial such as, but not limited to, silicon nitride, siliconoxy-nitride, oxygen-rich silicon oxy-nitride or silicon-rich siliconoxy-nitride. In one embodiment, regions 604A and 604B of thecharge-trapping layer are formed at a temperature approximately in therange of 600-900 degrees Celsius. In a specific embodiment, thecharge-trapping layer is formed by using gases such as, but not limitedto, dichlorosilane (H₂SiCl₂), bis-(tert-butylamino)silane (BTBAS),ammonia (NH₃) or nitrous oxide (N₂0). In one embodiment, the chargetrapping layer is formed to a total thickness approximately in the rangeof 5-15 nanometers and region 604B accounts for a thicknessapproximately in the range of 2-3 nanometers of the total thickness ofthe charge-trapping layer. In that embodiment, region 604A accounts forthe remaining total thickness of the charge-trapping layer, i.e. region604A accounts for the portion of the charge-trapping layer that is notsubsequently consumed to form a top or blocking dielectric layer.

In another aspect of the present invention, the charge-trapping layermay include multiple composition regions. For example, in accordancewith an embodiment of the present invention, the charge-trapping layerincludes an oxygen-rich portion and a silicon-rich portion and is formedby depositing an oxygen-rich oxy-nitride film by a first composition ofgases and, subsequently, depositing a silicon-rich oxy-nitride film by asecond composition of gases. In one embodiment, the charge-trappinglayer is formed by modifying the flow rate of ammonia (NH3) gas, andintroducing nitrous oxide (N20) and dichlorosilane (SiH2Cb) to providethe desired gas ratios to yield first an oxygen-rich oxy-nitride filmand then a silicon-rich oxy-nitride film. In a specific embodiment, theoxygen-rich oxy-nitride film is formed by introducing a process gasmixture including N20, NH3 and SiH2Cb, while maintaining the processchamber at a pressure approximately in the range of 5-500 mTorr, andmaintaining substrate 600 at a temperature approximately in the range of700-850 degrees Celsius, for a period approximately in the range of2.5-20 minutes. In a further embodiment, the process gas mixtureincludes N₂O and NH₃ having a ratio of from about 8:1 to about 1:8 andSiH₂Cl₂ and NH₃ having a ratio of from about 1:7 to about 7:1, and canbe introduced at a flow rate approximately in the range of 5-200standard cubic centimeters per minute (sccm). In another specificembodiment, the silicon-rich oxy-nitride film is formed by introducing aprocess gas mixture including N20, NH3 and SiH2Cb, while maintaining thechamber at a pressure approximately in the range of 5-500 mTorr, andmaintaining substrate 600 at a temperature approximately in the range of700-850 degrees Celsius, for a period approximately in the range of2.5-20 minutes. In a further embodiment, the process gas mixtureincludes N 20 and NH3 having a ratio of from about 8:1 to about 1:8 andSiH2Cb and NH3 mixed in a ratio of from about 1:7 to about 7:1,introduced at a flow rate of from about 5 to about 20 seem. Inaccordance with an embodiment of the present invention, thecharge-trapping layer comprises a bottom oxygen-rich silicon oxy-nitrideportion having a thickness approximately in the range of 2.5-3.5nanometers and a top silicon-rich silicon oxy-nitride portion having athickness approximately in the range of 9-10 nanometers. In oneembodiment, a region 504B of charge-trapping layer accounts for athickness approximately in the range of 2-3 nanometers of the totalthickness of the top silicon-rich silicon oxy-nitride portion of thecharge-trapping layer. Thus, region 604B, which is targeted forsubsequent consumption to form a second dielectric layer, may becomposed entirely of silicon-rich silicon oxy-nitride.

FIG. 6D illustrates a cross-sectional view of a substrate having asecond dielectric layer formed thereon, corresponding to operation 510from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention. Referring to operation 510 of Flowchart 500 andcorresponding FIG. 6D, a second dielectric layer 606 is formed oncharge-trapping layer 604. In an embodiment, the formation of seconddielectric layer 606 is carried out in the same process chamber used toform first dielectric layer 602 and the charge-trapping layer, withoutremoving substrate 600 from the process chamber between process steps.In one embodiment, the second radical oxidation process is carried outfollowing a nitrogen or argon purge of the process chamber following thedeposition of the charge-trapping layer.

Second dielectric layer 606 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. Second dielectriclayer 606 may be referred to in the art as a blocking dielectric layeror a top dielectric layer. In accordance with an embodiment of thepresent invention, second dielectric layer 606 is formed by consumingregion 604B of the charge-trapping layer formed in operation 508,described in association with FIG. 6C. Thus, in one embodiment, region604B is consumed to provide second dielectric layer 606, while region604A remains a charge-trapping layer 604. In a specific embodiment,region 604B is a silicon-rich silicon oxy-nitride region having athickness approximately in the range of 2-3 nanometers and is oxidizedto form second dielectric layer 606 having a thickness approximately inthe range of 3.5-4.5 nanometers. In that embodiment, second dielectriclayer 606 is composed of silicon dioxide. In accordance with anembodiment of the present invention, second dielectric layer 606 isformed by a second radical oxidation process, similar to the radicaloxidation process carried out to form blocking dielectric layer 406,described in association with FIG. 4B. In one embodiment, referring tooperation 512 of Flowchart 500, subsequent to forming second dielectriclayer 606, second dielectric layer 606 is further subjected to anitridation process similar to the nitridation process described inassociation with operation 506 from Flowchart 500. In a specificembodiment, the nitridation occurs following a nitrogen or argon purgeof the process chamber following the second radical oxidation process.Alternatively, this nitridation step may be skipped. In accordance withan embodiment of the present invention, no additional depositionprocesses are used in the formation of second dielectric layer 606.

Thus, in accordance with an embodiment of the present invention, an ONOstack including first dielectric layer 602, charge-trapping layer 604and second dielectric layer 606 is formed in a single pass in a processchamber. By fabricating these layers in a single pass of multiple wafersin the process chamber, high throughput requirements may be met whilestill ensuring the formation of very high quality films. Uponfabrication of an ONO stack including first dielectric layer 602,charge-trapping layer 604 and second dielectric layer 606, a nonvolatilecharge trap memory device may be fabricated to include a patternedportion of the ONO stack. FIG. 6E illustrates a cross-sectional view ofa nonvolatile charge trap memory device, in accordance with anembodiment of the present invention.

Referring to FIG. 6E, a nonvolatile charge trap memory device includes apatterned portion of the ONO stack formed over substrate 600. The ONOstack includes first dielectric layer 602, charge-trapping layer 604 andsecond dielectric layer 606. A gate layer 608 is disposed on seconddielectric layer 606. The nonvolatile charge trap memory device furtherincludes source and drain regions 612 in substrate 600 on either side ofthe ONO stack, defining a channel region 614 in substrate 600 underneaththe ONO stack. A pair of dielectric spacers 610 isolates the sidewallsof first dielectric layer 602, charge-trapping layer 604, seconddielectric layer 606 and gate layer 608. In a specific embodiment,channel region 614 is doped P-type and, in an alternative embodiment,channel region 614 is doped N-type.

In accordance with an embodiment of the present invention, thenonvolatile charge trap memory device described in association with FIG.6E is a SONOS-type device. By convention, SONOS stands for“Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first“Semiconductor” refers to the channel region material, the first “Oxide”refers to the tunnel dielectric layer, “Nitride” refers to thecharge-trapping dielectric layer, the second “Oxide” refers to the topdielectric layer (also known as a blocking dielectric layer) and thesecond “Semiconductor” refers to the gate layer. Thus, in accordancewith an embodiment of the present invention, first dielectric layer 602is a tunnel dielectric layer and second dielectric layer 606 is ablocking dielectric layer.

Gate layer 608 may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of a SONOS-type transistor. In accordance with an embodiment of the presentinvention, gate layer 608 is formed by a chemical vapor depositionprocess and is composed of doped poly-crystalline silicon. In anotherembodiment, gate layer 608 is formed by physical vapor deposition and iscomposed of a metal-containing material which may include, but is notlimited to, metal nitrides, metal carbides, metal silicides, hafnium,zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum,cobalt or nickel.

Source and drain regions 612 in substrate 600 may be any regions havingopposite conductivity to channel region 614. For example, in accordancewith an embodiment of the present invention, source and drain regions612 are N-type doped regions while channel region 614 is a P-type dopedregion. In one embodiment, substrate 600 and, hence, channel region 614,is composed of boron-doped single-crystal silicon having a boronconcentration in the range of 1×10¹⁵-1×10¹⁹ atoms/cm³. In thatembodiment, source and drain regions 612 are composed of phosphorous- orarsenic doped regions having a concentration of N-type dopants in therange of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specific embodiment, source anddrain regions 612 have a depth in substrate 600 in the range of 80-200nanometers. In accordance with an alternative embodiment of the presentinvention, source and drain regions 612 are P-type doped regions whilechannel region 614 is an N-type doped region.

In another aspect of the present invention, a dielectric layer formed byradical oxidation of the top surface of a substrate in an oxidationchamber may be less susceptible to crystal plane orientation differencesin the substrate upon which it is grown. For example, in one embodiment,the cornering effect caused by differential crystal plane oxidationrates is significantly reduced by forming a dielectric layer by aradical oxidation process. FIG. 7 A illustrates a cross-sectional viewof a substrate including first and second exposed crystal planes, inaccordance with an embodiment of the present invention.

Referring to FIG. 7 A, a substrate 700 has isolation regions 702 formedthereon. Substrate 700 may be composed of a material described inassociation with substrate 600 from FIG. 6A. Isolation regions 702 maybe composed of an insulating material suitable for adhesion to substrate700. An exposed portion of substrate 700 extends above the top surfaceof isolation regions 702. In accordance with an embodiment of thepresent invention, the exposed portion of substrate 700 has a firstexposed crystal plane 704 and a second exposed crystal plane 706. In oneembodiment, the crystal orientation of first exposed crystal plane 704is different from the crystal orientation of second exposed crystalplane 706. In a specific embodiment, substrate 700 is composed ofsilicon, first exposed crystal plane 704 has <1 00> orientation, andsecond exposed crystal plane 706 has <110> orientation.

Substrate 700 may be subjected to a radical oxidation process to form adielectric layer by consuming (oxidizing) the top surface of substrate700. In one embodiment, the oxidizing of substrate 700 by a radicaloxidation process includes oxidizing with a radical selected from thegroup consisting of an OH radical, an H02 radical or an 0 diradical.FIG. 7B illustrates a cross-sectional view of substrate 700 includingfirst and second crystal planes 704 and 706, respectively, and having adielectric layer 708 formed thereon, in accordance with an embodiment ofthe present invention. In an embodiment, first portion 708A ofdielectric layer 708 is formed on first exposed crystal plane 704 and asecond portion 708B of dielectric layer 708 is formed on second exposedcrystal plane 706, as depicted in FIG. 7B. In one embodiment, thethickness T10 f first portion 708A of dielectric layer 708 isapproximately equal to the thickness T2 of second portion 708B ofdielectric layer 708, even though the crystal plane orientation of firstexposed crystal plane 704 and second exposed crystal plane 706 differ.In a specific embodiment, the radical oxidation of substrate 700 iscarried out at a temperature approximately in the range of 600-900degrees Celsius. In a specific embodiment, the radical oxidation ofsubstrate 700 is carried out at a temperature approximately in the rangeof 700-800 degrees Celsius at a pressure approximately in the range of0.5-5 Torr.

Thus, a method for fabricating a nonvolatile charge trap memory devicehas been disclosed. In accordance with an embodiment of the presentinvention, a substrate is provided having a charge-trapping layerdisposed thereon. A portion of the charge-trapping layer is thenoxidized to form a blocking dielectric layer above the charge-trappinglayer by exposing the charge-trapping layer to a radical oxidationprocess.

In another aspect of the present invention, it may be desirable to use acluster tool to carry out a radical oxidation process. Accordingly,disclosed herein is a method to fabricate a nonvolatile charge trapmemory device. A substrate may first be subjected to a first radicaloxidation process to form a first dielectric layer in a first processchamber of a cluster tool. In one embodiment, a charge-trapping layer isthen deposited above the first dielectric layer in a second processchamber of the cluster tool. The charge-trapping layer may then besubjected to a second radical oxidation process to form a seconddielectric layer above the charge-trapping layer. In one embodiment, thesecond dielectric layer is formed by oxidizing a portion of thecharge-trapping layer in the first process chamber of the cluster tool.In a specific embodiment, the cluster tool is a single-wafer clustertool.

Formation of a dielectric layer in a chamber of a cluster tool maypermit the growth of the dielectric layer at temperatures higher thannormally achievable in batch processing chambers. Furthermore, a radicaloxidation process may be carried out in the chamber of the cluster toolas the primary pathway for growing the dielectric layer. In accordancewith an embodiment of the present invention, a radical oxidation processinvolving flowing hydrogen (H2) and oxygen (02) gas into an oxidationchamber of a cluster tool is carried out to effect growth of adielectric layer by oxidation consumption of an exposed substrate orfilm. In one embodiment, multiple radical oxidation processes arecarried out in an oxidation chamber of a cluster tool to provide atunnel dielectric layer and a blocking dielectric layer for anon-volatile charge trap memory device. These dielectric layers may beof very high quality, even at a reduced thickness. In one embodiment,the tunnel dielectric layer and the blocking dielectric layer are bothdenser and are composed of substantially fewer hydrogen atoms/cm3 than atunnel dielectric layer or a blocking dielectric layer formed in a batchprocess chamber. Furthermore, the substrate upon which a tunneldielectric layer and a blocking dielectric layer are formed may beexposed to a shorter temperature ramp rate and stabilization time in anoxidation chamber of a cluster tool as compared with a batch processchamber. Thus, in accordance with an embodiment of the present inventionembodiment, the impact on the thermal budget of the substrate is reducedby employing a radical oxidation process in an oxidation chamber of acluster tool. In accordance with another embodiment of the presentinvention, a dielectric layer formed by carrying out a radical oxidationprocess in an oxidation chamber of a cluster tool is less susceptible tocrystal plane orientation differences in the substrate from which it isgrown. In one embodiment, the cornering effect caused by differentialcrystal plane oxidation rates is significantly reduced by forming adielectric layer via a radical oxidation process carried out in anoxidation chamber of a cluster tool.

A portion of a nonvolatile charge trap memory device may be fabricatedin a cluster tool. FIG. 8 illustrates an arrangement of process chambersin a cluster tool, in accordance with an embodiment of the presentinvention. Referring to FIG. 8, an arrangement of process chambers in acluster tool 800 includes a transfer chamber 802, a first processchamber 804, a second process chamber 806 and a third process chamber808. In an embodiment, transfer chamber 802 is for receiving a waferfrom an external environment for introduction into cluster tool 800. Inone embodiment, each of the process chambers 802, 804 and 806 arearranged in a way such that a wafer may be passed back-and forth betweenthese chambers and transfer chamber 802, as depicted by thedouble-headed arrows in FIG. 8. In accordance with an additionalembodiment of the present invention, although not shown, cluster tool800 may be configured such that a wafer can be transferred directlybetween any pairing of process chambers 802, 804 or 806.

Cluster tool 800 may be any cluster tool for which an outsideenvironment is excluded in and between process chambers 804, 806 and 808and transfer chamber 802. Thus, in accordance with an embodiment of thepresent invention, once a wafer has entered process chamber 802, it isprotected from an external environment as it is moved into and betweenprocess chambers 804, 806 and 808 and transfer chamber 802. An exampleof such a cluster tool is the Centura® platform commercially availablefrom Applied Materials, Inc., located in Santa Clara, Calif. In oneembodiment, once a wafer has been received by transfer chamber 802, avacuum of less than approximately 100 mTorr is maintained in clustertool 800. In accordance with an embodiment of the present invention,cluster tool 800 incorporates a chuck (or multiple chucks, e.g., onechuck for each chamber) upon which the flat surface, as opposed to theedge surface, of a wafer rests on the chuck for processing and transferevents. In one embodiment, by having the flat surface of a wafer rest onthe chuck, more rapid ramp rates for heating the wafer are achievable byheating the wafer via the chuck. In a specific embodiment, cluster tool800 is a single-wafer cluster tool.

Process chambers 802, 804 and 806 may include, but are not limited to,oxidation chambers, low-pressure chemical vapor deposition chambers, ora combination thereof. For example, in accordance with an embodiment ofthe present invention, first process chamber 804 is a first oxidationchamber, second process chamber 806 is a low-pressure chemical vapordeposition chamber, and third process chamber 808 is a second oxidationchamber. An example of an oxidation chamber is the In-Situ SteamGeneration (ISSG) chamber from Applied Materials, Inc. Examples oflow-pressure chemical vapor deposition chambers include a SiNgen™chamber and an OXYgen™ chamber from Applied Materials, Inc. Instead ofheating entire process chambers to heat a wafer, which is the case fortypical batch process chambers, a chuck used for carrying a single wafermay be heated to heat the wafer. In accordance with an embodiment of thepresent invention, a chuck is used to heat a wafer to the desiredprocess temperature. Thus, relatively short temperature ramp times andstabilization times may be achieved.

A portion of a nonvolatile charge trap memory device may be fabricatedin a cluster tool. FIG. 9 depicts a Flowchart 900 representing a seriesof operations in a method for fabricating a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention. FIGS. 10A-10E illustrates cross-sectional views representingoperations in the fabrication of a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention.

Referring to FIG. 10A, a substrate 1000 is provided in a cluster tool.In one embodiment, substrate 1000 is provided in a transfer chamber,such as transfer chamber 802 described in association with FIG. 8.

Substrate 1000 may be composed of any material suitable forsemiconductor device fabrication. In one embodiment, substrate 1000 is abulk substrate composed of a single crystal of a material which mayinclude, but is not limited to, silicon, germanium, silicon-germanium ora III-V compound semiconductor material. In another embodiment,substrate 1000 includes a bulk layer with a top epitaxial layer. In aspecific embodiment, the bulk layer is composed of a single crystal of amaterial which may include, but is not limited to, silicon, germanium,silicon-germanium, a III-V compound semiconductor material or quartz,while the top epitaxial layer is composed of a single crystal layerwhich may include, but is not limited to, silicon, germanium,silicon-germanium or a III-V compound semiconductor material. In anotherembodiment, substrate 1000 includes a top epitaxial layer on a middleinsulator layer which is above a lower bulk layer. The top epitaxiallayer is composed of a single crystal layer which may include, but isnot limited to, silicon (i.e. to form a silicon-on-insulator (SOl)semiconductor substrate), germanium, silicon-germanium or a III-Vcompound semiconductor material. The insulator layer is composed of amaterial which may include, but is not limited to, silicon dioxide,silicon nitride or silicon oxy-nitride. The lower bulk layer is composedof a single crystal which may include, but is not limited to, silicon,germanium, silicon-germanium, a III-V compound semiconductor material orquartz. Substrate 1000 may further include dopant impurity atoms.

FIG. 10B illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 902from the Flowchart of FIG. 9, in accordance with an embodiment of thepresent invention. Referring to operation 902 of Flowchart 900 andcorresponding FIG. 10B, substrate 1000 is subjected to a first radicaloxidation process in a first process chamber of the cluster tool to forma first dielectric layer 1002.

First dielectric layer 1002 may be composed of a material and have athickness suitable to allow charge carriers to tunnel into asubsequently formed charge trapping layer under an applied gate bias,while maintaining a suitable barrier to leakage when a subsequentlyformed nonvolatile charge trap memory device is unbiased. In accordancewith an embodiment of the present invention, first dielectric layer 1002is formed by an oxidation process where the top surface of substrate1000 is consumed. Thus, in an embodiment, first dielectric layer 1002 iscomposed of an oxide of the material of substrate 1000. For example, inone embodiment, substrate 1000 is composed of silicon and firstdielectric layer 1002 is composed of silicon dioxide. In a specificembodiment, first dielectric layer 1002 is formed to a thicknessapproximately in the range of 1-10 nanometers. In a particularembodiment, first dielectric layer 1002 is formed to a thicknessapproximately in the range of 1.5-2.5 nanometers.

First dielectric layer 1002 may be formed by a radical oxidationprocess. In accordance with an embodiment of the present invention, theradical oxidation process involves flowing hydrogen (Hz) and oxygen (Oz)gas into an oxidation chamber, such as the oxidation chambers 804 or 808described in association with FIG. 8. In one embodiment, the partialpressures of Hz and Oz have a ratio to one another approximately in therange of 1:50-1:5. However, in an embodiment, an ignition event is notcarried out which would otherwise typically be used to pyrolyze the Hzand Oz to form steam. Instead, Hz and Oz are permitted to react to formradicals at the surface of substrate 1000. In one embodiment, theradicals are used to consume the top portion of substrate 1000 toprovide first dielectric layer 1002. In a specific embodiment, theradical oxidation process includes oxidizing with a radical such as, butnot limited to, an OH radical, an HO₂ radical or an O diradical. In aparticular embodiment, the radical oxidation process is carried out at atemperature approximately in the range of 950-1100 degrees Celsius at apressure approximately in the range of 5-15 Torr. In one embodiment, theradical oxidation process is carried out for a duration of approximatelyin the range of 1-3 minutes. In accordance with an embodiment of thepresent invention, first dielectric layer 1002 is formed as ahigh-density, low-hydrogen-content film.

Referring to operation 904 of Flowchart 900, subsequent to forming firstdielectric layer 1002, but prior to any further processing, firstdielectric layer 1002 may be subjected to a nitridation process. In anembodiment, the nitridation process is carried out in the same processchamber used to form first dielectric layer 1002. In one embodiment,first dielectric layer 1002 is annealed in the first process chamber,wherein the annealing includes heating substrate 1000 in an atmosphereincluding nitrogen at a temperature approximately in the range of900-1100 degrees Celsius for a duration approximately in the range of 30seconds-60 seconds. In one embodiment, the atmosphere including nitrogenis composed of a gas such as, but not limited to, nitrogen (N2), nitrousoxide (N20), nitrogen dioxide (N02), nitric oxide (NO) or ammonia (NH3).In another embodiment, the nitridation occurs in a separate processchamber. Alternatively, this nitridation step may be skipped.

FIG. 10C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 906from the Flowchart of FIG. 9, in accordance with an embodiment of thepresent invention. Referring to operation 906 of Flowchart 900 andcorresponding FIG. 10C, a charge-trapping layer having a first region1004A and a second region 1004B is formed on first dielectric layer 1002in the second process chamber of a cluster tool.

The charge-trapping layer may be composed of a material and have athickness suitable to store charge and, hence, change the thresholdvoltage of a subsequently formed gate stack. In accordance with anembodiment of the present invention, the charge-trapping layer iscomposed of two regions 1004A and 1004B, as depicted in FIG. 10C. In anembodiment, region 1 004A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 1004 B of the as-formedcharge-trapping layer will be consumed to form a second dielectriclayer, above region 1004A. In one embodiment, regions 1004A and 1004B ofthe charge-trapping layer are formed in the same process step and arecomposed of the same material.

The charge-trapping layer having regions 1004A and 1004B may be formedby a chemical vapor deposition process. In accordance with an embodimentof the present invention, the charge-trapping layer is composed of amaterial such as, but not limited to, silicon nitride, siliconoxy-nitride, oxygen-rich silicon oxy-nitride or silicon-rich siliconoxynitride. In an embodiment, the charge-trapping layer is formed onfirst dielectric layer 1002 in a low-pressure chemical vapor depositionchamber, such as the SiNgen™ low-pressure chemical vapor depositionchamber described in association with process chamber 806 from FIG. 8.In one embodiment, the second process chamber is a low-pressure chemicalvapor deposition chamber and regions 1004A and 1004B of thecharge-trapping layer are formed at a temperature less than thetemperature used to form first dielectric layer 1002. In a specificembodiment, regions 1004A and 1004B of the charge-trapping layer areformed at a temperature approximately in the range of 700-850 degreesCelsius. In an embodiment, the second process chamber is a low-pressurechemical vapor deposition chamber and the charge-trapping layer isformed by using gases such as, but not limited to, dichlorosilane(H₂SiCl₂), bis-(tert-butylamino) silane (BTBAS), ammonia (NH₃) ornitrous oxide (N₂O). In accordance with an embodiment of the presentinvention, the charge-trapping layer is formed to a total thicknessapproximately in the range of 5-15 nanometers and region 1004 B accountsfor a thickness approximately in the range of 2-3 nanometers of thetotal thickness of the charge-trapping layer. In that embodiment, region1 004A accounts for the remaining total thickness of the charge-trappinglayer, i.e. the portion of the charge-trapping layer that is notsubsequently consumed to form a top or blocking dielectric layer.

In another aspect of the present invention, the charge-trapping layermay include multiple composition regions. For example, in accordancewith an embodiment of the present invention, the charge-trapping layerincludes an oxygen-rich portion and a silicon-rich portion and is formedby depositing an oxygen-rich oxy-nitride film by a first composition ofgases in the second process chamber and, subsequently, depositing asilicon-rich oxy-nitride film by a second composition of gases in thesecond process chamber. In one embodiment, the charge-trapping layer isformed by modifying the flow rate of ammonia (NH3) gas, and introducingnitrous oxide (N20) and dichlorosilane (SiH2Cb) to provide the desiredgas ratios to yield first an oxygen-rich oxy-nitride film and then asilicon-rich oxy-nitride film. In a specific embodiment, the oxygen-richoxynitride film is formed by introducing a process gas mixture includingN20, NH3 and SiH2Cb, while maintaining the chamber at a pressureapproximately in the range of 0.5-500 Torr, and maintaining substrate1000 at a temperature approximately in the range of 700-850 degreesCelsius, for a period approximately in the range of 2.5-20 minutes. In afurther embodiment, the process gas mixture includes N20 and NH3 havinga ratio of from about 8:1 to about 1:8 and SiH2Cb and NH3 having a ratioof from about 1:7 to about 7:1, and can be introduced at a flow rateapproximately in the range of 5-200 standard cubic centimeters perminute (seem). In another specific embodiment, the silicon-richoxy-nitride film is formed by introducing a process gas mixtureincluding N20, NH3 and SiH2Cb, while maintaining the chamber at apressure approximately in the range of 0.5-500 Torr, and maintainingsubstrate 1000 at a temperature approximately in the range of 700-850degrees Celsius, for a period approximately in the range of 2.5-20minutes. In a further embodiment, the process gas mixture includes N20and NH3 having a ratio of from about 8:1 to about 1:8 and SiH2Cb and NH3mixed in a ratio of from about 1:7 to about 7:1, introduced at a flowrate of from about 5 to about 20 seem. In accordance with an embodimentof the present invention, the charge-trapping layer comprises a bottomoxygen-rich silicon oxy-nitride portion having a thickness approximatelyin the range of 2.5-3.5 nanometers and a top silicon-rich siliconoxynitride portion having a thickness approximately in the range of 9-10nanometers. In one embodiment, a region 1 004B of charge-trapping layeraccounts for a thickness approximately in the range of 2-3 nanometers ofthe total thickness of the top silicon-rich silicon oxy-nitride portionof the charge-trapping layer. Thus, region 1004B, which is targeted forsubsequent consumption to form a second dielectric layer, may becomposed entirely of silicon-rich silicon oxy-nitride.

FIG. 10D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 908 from theFlowchart of FIG. 9, in accordance with an embodiment of the presentinvention. Referring to operation 908 of Flowchart 900 and correspondingFIG. 10D, a second dielectric layer 1006 is formed on charge-trappinglayer 1004 in the first process chamber of the cluster tool.

Second dielectric layer 1006 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. In accordance with anembodiment of the present invention, second dielectric layer 1006 isformed by consuming region 1004B of the charge trapping layer formed inoperation 906, described in association with FIG. 10C. Thus, in oneembodiment region 1004B is consumed to provide second dielectric layer1006, while region 1004A remains a charge-trapping layer 1004. In aspecific embodiment, region 1004B is a silicon-rich silicon oxy-nitrideregion having a thickness approximately in the range of 2-3 nanometersand is oxidized to form second dielectric layer 1006 having a thicknessapproximately in the range of 3.5-4.5 nanometers. In that embodiment,second dielectric layer 1006 is composed of silicon dioxide.

Second dielectric layer 1006 may be formed by a second radical oxidationprocess. In accordance with an embodiment of the present invention, thesecond radical oxidation process involves flowing hydrogen (Hz) andoxygen (Oz) gas into an oxidation chamber, such as the oxidationchambers 804 or 808 described in association with FIG. 8. In oneembodiment, the partial pressures of Hz and Oz have a ratio to oneanother approximately in the range of 1:50-1:5. However, in anembodiment, an ignition event is not carried out which would otherwisetypically be used to pyrolyze the Hz and Oz to form steam. Instead, Hzand Oz are permitted to react to form radicals at the surface of region1 004 B. In one embodiment, the radicals are used to consume region 1004 B to provide second dielectric layer 1006. In a specific embodiment,the second radical oxidation process includes oxidizing with a radicalsuch as, but not limited to, an OH radical, an HO₂ radical or an Odiradical. In a particular embodiment, the second radical oxidationprocess is carried out at a temperature approximately in the range of950-1100 degrees Celsius at a pressure approximately in the range of5-15 Torr. In one embodiment, the second radical oxidation process iscarried out for a duration approximately in the range of 1-3 minutes. Inaccordance with an embodiment of the present invention, first dielectriclayer 1002 is formed as a high-density, low-hydrogen content film. Inone embodiment, no additional deposition step is required to form acomplete second dielectric layer 1006, as depicted in FIG. 10D and shownin Flowchart 900. Depending on wafer pass-through logistics in thecluster tool, the second radical oxidation process may be carried out inthe same, i.e. first, chamber as the first radical oxidation processused to form first dielectric layer 1002 or in a different, e.g. third,process chamber of the cluster tool. Thus, in accordance with anembodiment of the present invention, reference to a first processchamber can be used to mean reintroduction into the first processchamber or to mean introduction into a process chamber different fromthe first process chamber.

Referring to operation 910 of Flowchart 900, subsequent to formingsecond dielectric layer 1006, but prior to removing substrate 1000 fromthe cluster tool, second dielectric layer 1006 may be further subjectedto a nitridation process in the first process chamber. In accordancewith an embodiment of the present invention, the nitridation processincludes annealing second dielectric layer 1006 in an atmosphereincluding nitrogen at a temperature approximately in the range of900-1100 degrees Celsius for a duration approximately in the range of 30seconds-60 seconds. In one embodiment, the atmosphere including nitrogenis composed of a gas such as, but not limited to, nitrogen (N2), nitrousoxide (N20), nitrogen dioxide (N02), nitric oxide (NO) or ammonia (NH3).Alternatively, this nitridation step, i.e. operation 910 from Flowchart900, may be skipped and the wafer unloaded from the cluster tool.

Thus, in accordance with an embodiment of the present invention, an ONOstack including first dielectric layer 1002, charge-trapping layer 1004and second dielectric layer 1006 is formed in a single pass in a clustertool. By fabricating these layers in a single pass in the cluster tool,pristine interfaces between first dielectric layer 1002 andcharge-trapping layer 1004 and between charge-trapping layer 1004 andsecond dielectric layer 1006 may be preserved. In one embodiment, firstdielectric layer 1002, charge-trapping layer 1004 and second dielectriclayer 1006 are formed without breaking vacuum in the cluster tool. Inone embodiment, each layer is formed at a different temperature totailor film properties without incurring significant ramp timepenalties. Furthermore, by fabricating these layers in a cluster tool,as opposed to fabricating in batch processing tools, the overalluniformity of the stack of layers may be optimized. For example, inaccordance with an embodiment of the present invention, by fabricatinglayers 1002, 1004 and 1006 in a cluster tool, the variability inthickness of the stack of layers 1002, 1004 and 1006 across a singlewafer may be reduced by as much as approximately 30%. In an exemplaryembodiment, 1cr is approximately in the range of 1-2% of the thicknessof first dielectric layer 1002. In a specific embodiment, the clustertool is a single-wafer cluster tool.

Upon fabrication of an ONO stack including first dielectric layer 1002,charge-trapping layer 1004 and second dielectric layer 1006, anonvolatile charge trap memory device may be fabricated to include apatterned portion of the ONO stack. FIG. 10E illustrates across-sectional view of a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

Referring to FIG. 10E, a nonvolatile charge trap memory device includesa patterned portion of the ONO stack formed over substrate 1000. The ONOstack includes first dielectric layer 1002, charge-trapping layer 1004and second dielectric layer 1006. A gate layer 1008 is disposed onsecond dielectric layer 1006. The nonvolatile charge trap memory devicefurther includes source and drain regions 1012 in substrate 1000 oneither side of the ONO stack, defining a channel region 1014 insubstrate 1000 underneath the ONO stack. A pair of dielectric spacers1010 isolates the sidewalls of first dielectric layer 1002,charge-trapping layer 1004, second dielectric layer 1006 and gate layer1008. In a specific embodiment, channel region 1014 is doped P-type and,in an alternative embodiment, channel region 1014 is doped N-type.

In accordance with an embodiment of the present invention, thenonvolatile charge trap memory device described in association with FIG.10E is a SONOS-type device. By convention, SONOS stands for“Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first“Semiconductor” refers to the channel region material, the first “Oxide”refers to the tunnel dielectric layer, “Nitride” refers to thecharge-trapping dielectric layer, the second “Oxide” refers to the topdielectric layer (also known as a blocking dielectric layer) and thesecond “Semiconductor” refers to the gate layer. Thus, in accordancewith an embodiment of the present invention, first dielectric layer 1002is a tunnel dielectric layer and second dielectric layer 1006 is ablocking dielectric layer.

Gate layer 1008 may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of a SONOS-type transistor. In accordance with an embodiment of the presentinvention, gate layer 1008 is formed by a chemical vapor depositionprocess and is composed of doped poly-crystalline silicon. In anotherembodiment, gate layer 1008 is formed by physical vapor deposition andis composed of a metal-containing material which may include, but is notlimited to, metal nitrides, metal carbides, metal silicides, hafnium,zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum,cobalt or nickel.

Source and drain regions 1012 in substrate 1000 may be any regionshaving opposite conductivity to channel region 1014. For example, inaccordance with an embodiment of the present invention, source and drainregions 1012 are N-type doped regions while channel region 1014 is aP-type doped region. In one embodiment, substrate 1000 and, hence,channel region 1014, is composed of boron-doped single crystal siliconhaving a boron concentration in the range of 1×10¹⁵-1×10¹⁹ atoms/cm³. Inthat embodiment, source and drain regions 1012 are composed ofphosphorous- or arsenic-doped regions having a concentration of N-typedopants in the range of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specificembodiment, source and drain regions 1012 have a depth in substrate 1000in the range of 80-200 nanometers. In accordance with an alternativeembodiment of the present invention, source and drain regions 1012 areP-type doped regions while channel region 1014 is an-N-type dopedregion.

In another aspect of the present invention, a charge-trapping layer mayinclude multiple composition regions, where the composition regionclosest to a tunnel dielectric layer is subjected to a radical oxidationprocess. FIG. 11 depicts a Flowchart 1100 representing a series ofoperations in a method for fabricating a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention. FIGS.12A-12E illustrate cross-sectional views representing operations in thefabrication of a nonvolatile charge trap memory device, in accordancewith an embodiment of the present invention.

FIG. 12A illustrates a cross-sectional view of a substrate having afirst dielectric layer formed thereon, corresponding to operation 1102from the Flowchart of FIG. 11, in accordance with an embodiment of thepresent invention. Referring to operation 1102 of Flowchart 1100 andcorresponding FIG. 12A, substrate 1200 is subjected to a first radicaloxidation process in a first process chamber of a cluster tool to form afirst dielectric layer 1202. Substrate 1200 and first dielectric layer1202 may be composed of materials described in association withsubstrate 1 000 and first dielectric layer 1002 from FIGS. 10A and 10B,respectively. The radical oxidation process used to form firstdielectric layer 1202 may be similar to the radical oxidation processused to form first dielectric layer 1002, described in association withFIG. 10B.

Referring to operation 1104 of Flowchart 1100, subsequent to formingfirst dielectric layer 1202, but prior to any further processing, firstdielectric layer 1202 may be subjected to a nitridation process. Thenitridation process may be similar to the nitridation process describedin association with operation 904 of Flowchart 900. In one embodiment,the nitridation process is carried out in the same process chamber usedto form first dielectric layer 1202. In another embodiment, thenitridation occurs in a separate process chamber. Alternatively, thisnitridation step may be skipped.

FIG. 12B illustrates a cross-sectional view of a substrate having anoxygen-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 1106 from the Flowchart ofFIG. 11, in accordance with an embodiment of the present invention.Referring to operation 1106 of Flowchart 1100 and corresponding FIG.12B, an oxygen-rich silicon oxy-nitride portion 1204A is formed on firstdielectric layer 1202 in a second process chamber of the cluster tool.Oxygen-rich silicon oxy-nitride portion 1204A may be composed of anoxygen-rich silicon oxynitride material and formed by a techniquedescribed in association with first region 1 004A from FIG. 10C.

Referring to operation 1108 from Flowchart 1100, in accordance with anembodiment of the present invention, oxygen-rich silicon oxy-nitrideportion 1204A is subjected to a second radical oxidation process in thefirst process chamber of the cluster tool. The second radical oxidationprocess may be similar to one of the radical oxidation processes used toform first dielectric layer 1002 or second dielectric layer 1006,described in association with FIGS. 10B and 10D, respectively. In anembodiment, carrying out the second radical oxidation process is madepossible because oxygen-rich silicon oxy-nitride portion 1204A ismaintained in the environment within the tool and thus retains apristine surface. In one embodiment, the second radical oxidationprocess densifies oxygen-rich silicon oxy-nitride portion 1204A.Depending on wafer pass-through logistics in the cluster tool, thesecond radical oxidation process may be carried out in the same, i.e.first, chamber as the radical oxidation process used to form firstdielectric layer 1202 or in a different, e.g. third, process chamber.Thus, in accordance with an embodiment of the present invention,reference to a first process chamber can be used to mean reintroductioninto the first process chamber or to mean introduction into a processchamber different from the first process chamber.

FIG. 12C illustrates a cross-sectional view of a substrate having asilicon-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 1110 from the Flowchart ofFIG. 11, in accordance with an embodiment of the present invention.Referring to operation Ill 0 of Flowchart 1100 and corresponding FIG.12C, a silicon-rich silicon oxy-nitride portion having a first region1204B and a second region 1204C is formed on oxygen-rich siliconoxy-nitride portion 1204A in the second process chamber of the clustertool. The silicon-rich silicon oxynitride portion may be composed of asilicon-rich silicon oxy-nitride material and formed by a techniquedescribed in association with second region 1004B from FIG. 10C.Depending on wafer pass-through logistics in the cluster tool, thedeposition of silicon-rich silicon oxy-nitride portion of thecharge-trapping layer may be carried out in the same, i.e. second,chamber as the deposition of oxygen-rich silicon oxy-nitride portion1204A of the charge-trapping layer or in a different process chamber.Thus, in accordance with an embodiment of the present invention,reference to a second process chamber can be used to mean reintroductioninto the second process chamber or to mean introduction into a processchamber different from the second process chamber.

FIG. 12D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 1112 fromthe Flowchart of FIG. 11, in accordance with an embodiment of thepresent invention. Referring to operation 1112 of Flowchart 1100 andcorresponding FIG. 12D, a second dielectric layer 1206 is formed oncharge-trapping layer 1204 in the first process chamber of the clustertool. In accordance with an embodiment of the present invention, seconddielectric layer 1206 is formed by consuming second region 1204C of thesilicon-rich silicon oxy-nitride portion by a third radical oxidationprocess. Thus, in one embodiment, the remaining charge-trapping layer1204 between first dielectric layer 1202 and second dielectric layer1204 is composed of oxygen-rich silicon oxy-nitride portion 1204A andfirst region 1204B of the silicon-rich silicon oxy-nitride portion 1204,as depicted in FIG. 12D. The third radical oxidation process used toconsume second region 1204C of the silicon-rich silicon oxy-nitrideportion to provide second dielectric layer 1206 may be similar to theradical oxidation process used to form second dielectric layer 1006,described in association with FIG. 10D. Depending on wafer pass-throughlogistics in the cluster tool, the third radical oxidation process maybe carried out in the same, i.e. first, chamber as the radical oxidationprocess used to form first dielectric layer 1202 or in a different, e.g.third, process chamber. Thus, in accordance with an embodiment of thepresent invention, reference to a first process chamber can be used tomean reintroduction into the first process chamber or to meanintroduction into a process chamber different from the first processchamber.

Referring to operation 1114 of Flowchart 1100, subsequent to formingsecond dielectric layer 1206, but prior to removing substrate 1200 fromthe cluster tool, second dielectric layer 1206 may be further subjectedto a nitridation process in the first process chamber. The nitridationprocess may be similar to the nitridation process described inassociation with operation 910 from Flowchart 900. In one embodiment,the nitridation process is carried out in the same process chamber usedto form second dielectric layer 1206. In another embodiment, thenitridation occurs in a separate process chamber. Alternatively, thisnitridation step may be skipped.

Upon fabrication of an ONO stack including first dielectric layer 1202,charge-trapping layer 1204 and second dielectric layer 1206, anonvolatile charge trap memory device may be fabricated to include apatterned portion of the ONO stack. FIG. 12E illustrates across-sectional view of a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

Referring to FIG. 12E, a nonvolatile charge trap memory device includesa patterned portion of the ONO stack formed over substrate 1200. The ONOstack includes first dielectric layer 1202, charge-trapping layer 1204and second dielectric layer 1206. A gate layer 1208 is disposed onsecond dielectric layer 1206. The nonvolatile charge trap memory devicefurther includes source and drain regions 1212 in substrate 1200 oneither side of the ONO stack, defining a channel region 1214 insubstrate 1200 underneath the ONO stack. A pair of dielectric spacers1210 isolates the sidewalls of first dielectric layer 1202,charge-trapping layer 1204, second dielectric layer 1206 and gate layer1208. In accordance with an embodiment of the present invention,charge-trapping layer 1204 is composed of an oxygen-rich siliconoxy-nitride portion 1204A and a silicon-rich silicon oxy-nitride portion1204B, as depicted in FIG. 12E. In one embodiment, the nonvolatilecharge trap memory device is a SONOS-type device. Gate layer 1208,source and drain regions 1212 and channel region 1214 may be composed ofmaterials described in association with gate layer 1008, source anddrain regions 1012 and channel region 1014 from FIG. 10E.

In another aspect of the present invention, a dielectric layer formed byradical oxidation of the top surface of a substrate in an oxidationchamber may be less susceptible to crystal plane orientation differencesin the substrate upon which it is grown. For example, in one embodiment,the cornering effect caused by differential crystal plane oxidationrates is significantly reduced by forming a dielectric layer in anoxidation chamber of a cluster tool. FIG. 13A illustrates across-sectional view of a substrate including first and second exposedcrystal planes, in accordance with an embodiment of the presentinvention.

Referring to FIG. 13A, a substrate 1300 has isolation regions 1302formed thereon. Substrate 1300 may be composed of a material describedin association with substrate 1000 from FIG. 10A. Isolation regions 1302may be composed of an insulating material suitable for adhesion tosubstrate 1300. An exposed portion of substrate 1300 extends above thetop surface of isolation regions 1302. In accordance with an embodimentof the present invention, the exposed portion of substrate 1300 has afirst exposed crystal plane 1304 and a second exposed crystal plane1306. In one embodiment, the crystal orientation of first exposedcrystal plane 1304 is different from the crystal orientation of secondexposed crystal plane 1306. In a specific embodiment, substrate 1300 iscomposed of silicon, first exposed crystal plane 1304 has <1 00>orientation, and second exposed crystal plane 1306 has <110>orientation.

Substrate 1300 may be subjected to a radical oxidation process in acluster tool to form a dielectric layer by consuming (oxidizing) the topsurface of substrate 1300. In one embodiment, the oxidizing of substrate1300 by a radical oxidation process includes oxidizing with a radicalselected from the group consisting of an OH radical, an H02 radical oran 0 diradical. FIG. 13B illustrates a cross-sectional view of substrate1300 including first and second crystal planes 1304 and 1306,respectively, and having a dielectric layer 1308 formed thereon, inaccordance with an embodiment of the present invention. In anembodiment, first portion 1308A of dielectric layer 1308 is formed onfirst exposed crystal plane 1304 and a second portion 1308B ofdielectric layer 1308 is formed on second exposed crystal plane 1306, asdepicted in FIG. 13B. In one embodiment, the thickness T10 f firstportion 1308A of dielectric layer 1308 is approximately equal to thethickness T2 of second portion 1308B of dielectric layer 1308, eventhough the crystal plane orientation of first exposed crystal plane 1304and second exposed crystal plane 1306 differ. In a specific embodiment,the radical oxidation of substrate 1300 is carried out at a temperatureapproximately in the range of 950-1100 degrees Celsius at a pressureapproximately in the range of 5-15 Torr. In one embodiment, subsequentto forming dielectric layer 1308, substrate 1300 is annealed in theoxidation chamber in an atmosphere including nitrogen at a temperatureapproximately in the range of 900-1100 degrees Celsius for a durationapproximately in the range of 30 seconds-60 seconds.

Implementations and Alternatives

In one aspect the present disclosure is directed to memory devicesincluding an oxide split multi-layer charge storing structure. FIG. 14is a block diagram illustrating a cross-sectional side view of anembodiment of one such semiconductor memory device 1400. The memorydevice 1400 includes a SONONOS stack 1402 including an ONONO structure1404 formed over a surface 1406 of a substrate 1408. Substrate 1408includes one or more diffusion regions 1410, such as source and drainregions, aligned to the gate stack 1402 and separated by a channelregion 1412. Generally, the SONONOS structure 1402 includes apolysilicon or metal gate layer 1414 formed upon and in contact with theONONO structure 1404. The gate 1414 is separated or electricallyisolated from the substrate 1408 by the ONONO structure 1404. The ONONOstructure 1404 includes a thin, lower oxide layer or tunneling oxidelayer 1416 that separates or electrically isolates the stack 1402 fromthe channel region 1412, a top or blocking oxide layer 1420, and amulti-layer charge storing layer 1404. The multi-layer charge storinglayer generally includes at least two nitride layers having differingcompositions of silicon, oxygen and nitrogen, including a silicon-rich,nitrogen-rich, and oxygen-lean top nitride layer 1418, a silicon-rich,oxygen-rich, the bottom nitride layer 1419, and an oxide, anti-tunnelinglayer 1421.

It has been found that a silicon-rich, oxygen-rich, bottom nitride layer1419 decreases the charge loss rate after programming and after erase,which is manifested in a small voltage shift in the retention mode,while a silicon-rich, nitrogen-rich, and oxygen-lean top nitride layer1418 improves the speed and increases of the initial difference betweenprogram and erase voltage without compromising a charge loss rate ofmemory devices made using an embodiment of thesilicon-oxide-oxynitride-oxide-silicon structure, thereby extending theoperating life of the device.

It has further been found the anti-tunneling layer 1421 substantiallyreduces the probability of electron charge that accumulates at theboundaries of the upper nitride layer 1418 during programming fromtunneling into the bottom nitride layer 1419, resulting in lower leakagecurrent than for the structure illustrated in FIG. 1.

The multi-layer charge storing layer can have an overall thickness offrom about 50 Å to about 150 Å, and in certain embodiments less thanabout 100 Å, with the with the thickness of the anti-tunneling layer1421 being from about 5 Å to about 20 Å, and the thicknesses of thenitride layers 1418, 1419, being substantially equal.

A method or forming or fabricating a split multi-layer charge storingstructure according to one embodiment will now be described withreference to the flowchart of FIG. 15.

Referring to FIG. 15, the method begins with forming a first oxidelayer, such as a tunneling oxide layer, over a silicon containing layeron a surface of a substrate (1500). As noted above, the tunneling oxidelayer can be formed or deposited by any suitable means, including aplasma oxidation process, In-Situ Steam Generation (ISSG) or a radicaloxidation process. In one embodiment, the radical oxidation processinvolves flowing hydrogen (H₂) and oxygen (O₂) gas into a processingchamber or furnace to effect growth of a the tunneling oxide layer byoxidation consumption of a portion of the substrate.

Next, the first or bottom nitride or nitride containing layer of themulti-layer charge storing layer is formed on a surface of the tunnelingoxide layer (1502). In one embodiment, the nitride layers are formed ordeposited in a low pressure CVD process using a silicon source, such assilane (SiH₄), chlorosilane (SiH₃Cl), dichlorosilane or DCS (SiH₂Cl₂),tetrachlorosilane (SiCl₄) or Bis-TertiaryButylAmino Silane (BTBAS), anitrogen source, such as nitrogen (N₂), ammonia (NH₃), nitrogen trioxide(NO₃) or nitrous oxide (N₂O), and an oxygen-containing gas, such asoxygen (O₂) or N₂O. Alternatively, gases in which hydrogen has beenreplaced by deuterium can be used, including, for example, thesubstitution of deuterated-ammonia (ND₃) for NH₃. The substitution ofdeuterium for hydrogen advantageously passivates Si dangling bonds atthe silicon-oxide interface, thereby increasing an NBTI (Negative BiasTemperature Instability) lifetime of the devices.

For example, the lower or bottom nitride layer can be deposited over thetunneling oxide layer by placing the substrate in a deposition chamberand introducing a process gas including N₂O, NH₃ and DCS, whilemaintaining the chamber at a pressure of from about 5 milliTorr (mT) toabout 500 mT, and maintaining the substrate at a temperature of fromabout 700 degrees Celsius to about 850 degrees Celsius and in certainembodiments at least about 760 degrees Celsius, for a period of fromabout 2.5 minutes to about 20 minutes. In particular, the process gascan include a first gas mixture of N₂O and NH₃ mixed in a ratio of fromabout 8:1 to about 1:8 and a second gas mixture of DCS and NH₃ mixed ina ratio of from about 1:7 to about 7:1, and can be introduced at a flowrate of from about 5 to about 200 standard cubic centimeters per minute(sccm). It has been found that an oxynitride layer produced or depositedunder these condition yields a silicon-rich, oxygen-rich, bottom nitridelayer.

Next, the anti-tunneling layer is formed or deposited on a surface ofthe bottom nitride layer (1504). As with the tunneling oxide layer, theanti-tunneling layer can be formed or deposited by any suitable means,including a plasma oxidation process, In-Situ Steam Generation (ISSG) ora radical oxidation process. In one embodiment, the radical oxidationprocess involves flowing hydrogen (H₂) and oxygen (O₂) gas into abatch-processing chamber or furnace to effect growth of theanti-tunneling layer by oxidation consumption of a portion of the bottomnitride layer.

The second or top nitride layer of the multi-layer charge storing layeris then formed on a surface of the anti-tunneling layer (1506). The topnitride layer can be deposited over the anti-tunneling layer 1421 in aCVD process using a process gas including N₂O, NH₃ and DCS, at a chamberpressure of from about 5 mT to about 500 mT, and at a substratetemperature of from about 700 degrees Celsius to about 850 degreesCelsius and in certain embodiments at least about 760 degrees Celsius,for a period of from about 2.5 minutes to about 20 minutes. Inparticular, the process gas can include a first gas mixture of N₂O andNH₃ mixed in a ratio of from about 8:1 to about 1:8 and a second gasmixture of DCS and NH₃ mixed in a ratio of from about 1:7 to about 7:1,and can be introduced at a flow rate of from about 5 to about 20 sccm.It has been found that an oxynitride layer produced or deposited underthese condition yields a silicon-rich, nitrogen-rich, and oxygen-leantop nitride layer 1418, which improves the speed and increases of theinitial difference between program and erase voltage withoutcompromising a charge loss rate of memory devices made using anembodiment of the silicon-oxide-oxynitride-oxide-silicon structure,thereby extending the operating life of the device.

In some embodiments, the silicon-rich, nitrogen-rich, and oxygen-leantop nitride layer can be deposited over the anti-tunneling layer in aCVD process using a process gas including BTBAS and ammonia (NH₃) mixedat a ratio of from about 7:1 to about 1:7 to further include aconcentration of carbon selected to increase the number of trapstherein. The selected concentration of carbon in the second oxynitridelayer can include a carbon concentration of from about 5% to about 15%.

Finally, a top, blocking oxide layer or HTO layer is formed on a surfaceof the second layer of the multi-layer charge storing layer (1508). Aswith the tunneling oxide layer and the anti-tunneling layer the HTOlayer can be formed or deposited by any suitable means, including aplasma oxidation process, In-Situ Steam Generation (ISSG) or a radicaloxidation process. In one embodiment, the HTO layer is formed using aplasma oxidation performed in a plasma process chamber. Typicaldeposition conditions used for this process are—R.F power in the range1500 W to 10000 W, H2 and O2 with H2 volume percent between 0% and 90%,substrate temperature between 300 C to 400 C, deposition time being 20to 60 sec

Alternatively, the HTO layer is formed using an ISSG oxidation process.In one embodiment, the ISSG is performed in an RTP chamber, such as theISSG chamber from Applied Materials described above, at pressures offrom about 8 to 12 Torr and a temperature of about 1050° C. with anoxygen rich gas mixture hydrogen to which from about 0.5% to 33%hydrogen has been added. The deposition time is in the range 20 to 60sec.

It will be appreciated that in either embodiment the thickness of thetop nitride layer may be adjusted or increased as some of the topnitride layer will be effectively consumed or oxidized during theprocess of forming the HTO layer.

Optionally, the method may further include forming or depositing a metalor polysilicon containing layer on a surface of the HTO layer to form agate layer of the transistor or device (1508). The gate layer can be,for example, a polysilicon layer deposited by a CVD process to form asilicon-oxide-nitride-oxide-nitride-oxide-silicon (SONOS) structure.

In another aspect the present disclosure is also directed to multigateor multigate-surface memory devices including charge-trapping regionsoverlying two or more sides of a channel formed on or above a surface ofa substrate, and methods of fabricating the same. Multigate devicesinclude both planar and non-planar devices. A planar multigate device(not shown) generally includes a double-gate planar device in which anumber of first layers are deposited to form a first gate below asubsequently formed channel, and a number of second layers are depositedthereover to form a second gate. A non-planar multigate device generallyincludes a horizontal or vertical channel formed on or above a surfaceof a substrate and surrounded on three or more sides by a gate.

FIG. 16A illustrates one embodiment of a non-planar multigate memorydevice including a charge-trapping region. Referring to FIG. 16A, thememory device 1600, commonly referred to as a finFET, includes a channel1602 formed from a thin film or layer of semiconducting materialoverlying a surface 1604 on a substrate 1606 connecting a source 1608and a drain 1610 of the memory device. The channel 1602 is enclosed onthree sides by a fin which forms a gate 1612 of the device. Thethickness of the gate 1612 (measured in the direction from source todrain) determines the effective channel length of the device.

In accordance with the present disclosure, the non-planar multigatememory device 1600 of FIG. 16A can include a split charge-trappingregion. FIG. 16B is a cross-sectional view of a portion of thenon-planar memory device of FIG. 16A including a portion of thesubstrate 1606, channel 1602 and the gate 1612 illustrating amulti-layer charge storing layer 1614. The gate 1612 further includes atunnel oxide layer 1616 overlying a raised channel 1602, a blockingdielectric 1618 and a metal gate layer 1620 overlying the blocking layerto form a control gate of the memory device 1600. In some embodiments adoped polysilicon may be deposited instead of metal to provide apolysilicon gate layer. The channel 1602 and gate 1612 can be formeddirectly on substrate 1606 or on an insulating or dielectric layer 1622,such as a buried oxide layer, formed on or over the substrate.

Referring to FIG. 16B, the multi-layer charge storing layer 1614includes at least one lower or bottom charge-trapping layer 1624including nitride closer to the tunnel oxide layer 1616, and an upper ortop charge-trapping layer 1626 overlying the bottom charge-trappinglayer. Generally, the top charge-trapping layer 1626 includes asilicon-rich, oxygen-lean nitride layer and includes a majority of acharge traps distributed in multiple charge-trapping layers, while thebottom charge-trapping layer 1624 includes an oxygen-rich nitride orsilicon oxynitride, and is oxygen-rich relative to the topcharge-trapping layer to reduce the number of charge traps therein. Byoxygen-rich it is meant wherein a concentration of oxygen in the bottomcharge-trapping layer 1624 is from about 15 to about 40%, whereas aconcentration of oxygen in top charge-trapping layer 1626 is less thanabout 5%.

In one embodiment, the blocking dielectric 1618 also includes an oxide,such as an HTO, to provide an ONNO structure. The channel 1602 and theoverlying ONNO structure can be formed directly on a silicon substrate1606 and overlaid with a doped polysilicon gate layer 1620 to provide aSONNOS structure.

In some embodiments, such as that shown in FIG. 16B, the multi-layercharge storing layer 1614 further includes at least one thin,intermediate or anti-tunneling layer 1628 including a dielectric, suchas an oxide, separating the top charge-trapping layer 1626 from thebottom charge-trapping layer 1624. As noted above, the anti-tunnelinglayer 1628 substantially reduces the probability of electron charge thataccumulates at the boundaries of the upper nitride layer 1626 duringprogramming from tunneling into the bottom nitride layer 1624.

As with the embodiments described above, either or both of the bottomcharge-trapping layer 1624 and the top charge-trapping layer 1626 caninclude silicon nitride or silicon oxynitride, and can be formed, forexample, by a CVD process including N₂O/NH₃ and DCS/NH₃ gas mixtures inratios and at flow rates tailored to provide a silicon-rich andoxygen-rich oxynitride layer. The second nitride layer of themulti-layer charge storing structure is then formed on the middle oxidelayer. The top charge-trapping layer 1626 has a stoichiometriccomposition of oxygen, nitrogen and/or silicon different from that ofthe bottom charge-trapping layer 1624, and may also be formed ordeposited by a CVD process using a process gas including DCS/NH₃ andN₂O/NH₃ gas mixtures in ratios and at flow rates tailored to provide asilicon-rich, oxygen-lean top nitride layer.

In those embodiments including an intermediate or anti-tunneling layer1628 including oxide, the anti-tunneling layer can be formed byoxidation of the bottom oxynitride layer, to a chosen depth usingradical oxidation. Radical oxidation may be performed, for example, at atemperature of 1000-1100 degrees Celsius using a single wafer tool, or800-900 degrees Celsius using a batch reactor tool. A mixture of H₂ andO₂ gasses may be employed at a pressure of 300-500 Tor for a batchprocess, or 10-15 Tor using a single vapor tool, for a time of 1-2minutes using a single wafer tool, or 30 min-1 hour using a batchprocess.

Finally, in those embodiments including a blocking dielectric 1618including oxide the oxide may be formed or deposited by any suitablemeans. In one embodiment the oxide of the blocking dielectric 1618 is ahigh temperature oxide deposited in a HTO CVD process. Alternatively,the blocking dielectric 1618 or blocking oxide layer may be thermallygrown, however it will be appreciated that in this embodiment the topnitride thickness may be adjusted or increased as some of the topnitride will be effectively consumed or oxidized during the process ofthermally growing the blocking oxide layer. A third option is to oxidizethe top nitride layer to a chosen depth using radical oxidation.

A suitable thickness for the bottom charge-trapping layer 1624 may befrom about 30 Å to about 160 Å (with some variance permitted, forexample ±10 A), of which about 5-20 Å may be consumed by radicaloxidation to form the anti-tunneling layer 1628. A suitable thicknessfor the top charge-trapping layer 1626 may be at least 30 Å. In certainembodiments, the top charge-trapping layer 1626 may be formed up to 130Å thick, of which 30-70 Å may be consumed by radical oxidation to formthe blocking dielectric 1618. A ratio of thicknesses between the bottomcharge-trapping layer 1624 and top charge-trapping layer 1626 isapproximately 1:1 in some embodiments, although other ratios are alsopossible.

In other embodiments, either or both of the top charge-trapping layer1626 and the blocking dielectric 1618 may include a high K dielectric.Suitable high K dielectrics include hafnium based materials such asHfSiON, HfSiO or HfO, Zirconium based material such as ZrSiON, ZrSiO orZrO, and Yttrium based material such as Y₂O₃.

In another embodiment, shown in FIGS. 17A and 17B, the memory device caninclude a nanowire channel formed from a thin film of semiconductingmaterial overlying a surface on a substrate connecting a source and adrain of the memory device. By nanowire channel it is meant a conductingchannel formed in a thin strip of crystalline silicon material, having amaximum cross-sectional dimension of about 10 nanometers (nm) or less,and more preferably less than about 6 nm. Optionally, the channel can beformed to have <100> surface crystalline orientation relative to a longaxis of the channel.

Referring to FIG. 17A, the memory device 1700 includes a horizontalnanowire channel 1702 formed from a thin film or layer of semiconductingmaterial on or overlying a surface on a substrate 1706, and connecting asource 1708 and a drain 1710 of the memory device. In the embodimentshown, the device has a gate-all-around (GAA) structure in which thenanowire channel 1702 is enclosed on all sides by a gate 1712 of thedevice. The thickness of the gate 1712 (measured in the direction fromsource to drain) determines the effective channel length of the device.

In accordance with the present disclosure, the non-planar multigatememory device 1700 of FIG. 17A can include a split charge-trappingregion. FIG. 17B is a cross-sectional view of a portion of thenon-planar memory device of FIG. 17A including a portion of thesubstrate 1706, nanowire channel 1702 and the gate 1712 illustrating asplit charge-trapping region. Referring to FIG. 17B, the gate 1712includes a tunnel oxide 1714 overlying the nanowire channel 1702, asplit charge-trapping region, a blocking dielectric 1716 and a gatelayer 1718 overlying the blocking layer to form a control gate of thememory device 1700. The gate layer 1718 can comprise a metal or a dopedpolysilicon. The split charge-trapping region includes at least oneinner charge-trapping layer 1720 comprising nitride closer to the tunneloxide 1714, and an outer charge-trapping layer 1722 overlying the innercharge-trapping layer. Generally, the outer charge-trapping layer 1722comprises a silicon-rich, oxygen-lean nitride layer and comprises amajority of a charge traps distributed in multiple charge-trappinglayers, while the inner charge-trapping layer 1720 comprises anoxygen-rich nitride or silicon oxynitride, and is oxygen-rich relativeto the outer charge-trapping layer to reduce the number of charge trapstherein.

In some embodiments, such as that shown, the split charge-trappingregion further includes at least one thin, intermediate oranti-tunneling layer 1724 comprising a dielectric, such as an oxide,separating outer charge-trapping layer 1722 from the innercharge-trapping layer 1720. The anti-tunneling layer 1724 substantiallyreduces the probability of electron charge that accumulates at theboundaries of outer charge-trapping layer 1722 during programming fromtunneling into the inner charge-trapping layer 1720, resulting in lowerleakage current.

As with the embodiment described above, either or both of the innercharge-trapping layer 1720 and the outer charge-trapping layer 1722 cancomprise silicon nitride or silicon oxynitride, and can be formed, forexample, by a CVD process including N₂O/NH₃ and DCS/NH₃ gas mixtures inratios and at flow rates tailored to provide a silicon-rich andoxygen-rich oxynitride layer. The second nitride layer of themulti-layer charge storing structure is then formed on the middle oxidelayer. The outer charge-trapping layer 1722 has a stoichiometriccomposition of oxygen, nitrogen and/or silicon different from that ofthe inner charge-trapping layer 1720, and may also be formed ordeposited by a CVD process using a process gas including DCS/NH₃ andN₂O/NH₃ gas mixtures in ratios and at flow rates tailored to provide asilicon-rich, oxygen-lean top nitride layer.

In those embodiments including an intermediate or anti-tunneling layer1724 comprising oxide, the anti-tunneling layer can be formed byoxidation of the inner charge-trapping layer 1720, to a chosen depthusing radical oxidation. Radical oxidation may be performed, forexample, at a temperature of 1000-1100 degrees Celsius using a singlewafer tool, or 800-900 degrees Celsius using a batch reactor tool. Amixture of H₂ and O₂ gasses may be employed at a pressure of 300-500 Torfor a batch process, or 10-15 Tor using a single vapor tool, for a timeof 1-2 minutes using a single wafer tool, or 30 min-1 hour using a batchprocess.

Finally, in those embodiments in which the blocking dielectric 1716comprises oxide, the oxide may be formed or deposited by any suitablemeans. In one embodiment the oxide of blocking dielectric 1716 is a hightemperature oxide deposited in a HTO CVD process. Alternatively, theblocking dielectric 1716 or blocking oxide layer may be thermally grown,however it will be appreciated that in this embodiment the thickness ofthe outer charge-trapping layer 1722 may need to be adjusted orincreased as some of the top nitride will be effectively consumed oroxidized during the process of thermally growing the blocking oxidelayer.

A suitable thickness for the inner charge-trapping layer 1720 may befrom about 30 Å to about 80 Å (with some variance permitted, for example±10 A), of which about 5-20 Å may be consumed by radical oxidation toform the anti-tunneling layer 1724. A suitable thickness for the outercharge-trapping layer 1722 may be at least 30 Å. In certain embodiments,the outer charge-trapping layer 1722 may be formed up to 170 Å thick, ofwhich 30-70 Å may be consumed by radical oxidation to form the blockingdielectric 1716. A ratio of thicknesses between the innercharge-trapping layer 1720 and the outer charge-trapping layer 1722 isapproximately 1:1 in some embodiments, although other ratios are alsopossible.

In other embodiments, either or both of the outer charge-trapping layer1722 and the blocking dielectric 1716 may comprise a high K dielectric.Suitable high K dielectrics include hafnium based materials such asHfSiON, HfSiO or HfO, Zirconium based material such as ZrSiON, ZrSiO orZrO, and Yttrium based material such as Y₂O₃.

FIG. 17C illustrates a cross-sectional view of a vertical string ofnon-planar multigate devices 1700 of FIG. 17A arranged in a Bit-CostScalable or BiCS architecture 1726. The architecture 1726 consists of avertical string or stack of non-planar multigate devices 1700, whereeach device or cell includes a channel 1702 overlying the substrate1706, and connecting a source and a drain (not shown in this figure) ofthe memory device, and having a gate-all-around (GAA) structure in whichthe nanowire channel 1702 is enclosed on all sides by a gate 1712. TheBiCS architecture reduces number of critical lithography steps comparedto a simple stacking of layers, leading to a reduced cost per memorybit.

In another embodiment, the memory device is or includes a non-planardevice comprising a vertical nanowire channel formed in or from asemiconducting material projecting above or from a number of conducting,semiconducting layers on a substrate. In one version of this embodiment,shown in cut-away in FIG. 18A, the memory device 1800 comprises avertical nanowire channel 1802 formed in a cylinder of semiconductingmaterial connecting a source 1804 and drain 1806 of the device. Thechannel 1802 is surrounded by a tunnel oxide 1808, a charge-trappingregion 1810, a blocking layer 1812 and a gate layer 1814 overlying theblocking layer to form a control gate of the memory device 1800. Thechannel 1802 can include an annular region in an outer layer of asubstantially solid cylinder of semiconducting material, or can includean annular layer formed over a cylinder of dielectric filler material.As with the horizontal nanowires described above, the channel 1802 cancomprise polysilicon or recrystallized polysilicon to form amonocrystalline channel. Optionally, where the channel 1802 includes acrystalline silicon, the channel can be formed to have <100> surfacecrystalline orientation relative to a long axis of the channel.

In some embodiments, such as that shown in FIG. 18B, the charge-trappingregion 1810 can be a split charge-trapping region including at least afirst or inner charge trapping layer 1816 closest to the tunnel oxide1808, and a second or outer charge trapping layer 1818. Optionally, thefirst and second charge trapping layers can be separated by anintermediate oxide or anti-tunneling layer 1820.

As with the embodiments described above, either or both of the firstcharge trapping layer 1816 and the second charge trapping layer 1818 cancomprise silicon nitride or silicon oxynitride, and can be formed, forexample, by a CVD process including N₂O/NH₃ and DCS/NH₃ gas mixtures inratios and at flow rates tailored to provide a silicon-rich andoxygen-rich oxynitride layer.

Finally, either or both of the second charge trapping layer 1818 and theblocking layer 1812 may comprise a high K dielectric, such as HfSiON,HfSiO, HfO, ZrSiON, ZrSiO, ZrO, or Y₂O₃.

A suitable thickness for the first charge trapping layer 1816 may befrom about 30 Å to about 80 Å (with some variance permitted, for example±10 A), of which about 5-20 Å may be consumed by radical oxidation toform the anti-tunneling layer 1820. A suitable thickness for the secondcharge trapping layer 1818 may be at least 30 Å, and a suitablethickness for the blocking dielectric 1812 may be from about 30-70 Å.

The memory device 1800 of FIG. 18A can be made using either a gate firstor a gate last scheme. FIGS. 19A-F illustrate a gate first scheme forfabricating the non-planar multigate device of FIG. 18A. FIGS. 20A-Fillustrate a gate last scheme for fabricating the non-planar multigatedevice of FIG. 18A.

Referring to FIG. 19A, in a gate first scheme a first or lowerdielectric layer 1902, such as a blocking oxide, is formed over a first,doped diffusion region 1904, such as a source or a drain, in a substrate1906. A gate layer 1908 is deposited over the first dielectric layer1902 to form a control gate of the device, and a second or upperdielectric layer 1910 formed thereover. As with embodiments describedabove, the first and second dielectric layers 1902, 1910, can bedeposited by CVD, radical oxidation or be formed by oxidation of aportion of the underlying layer or substrate. The gate layer 1908 cancomprise a metal deposited or a doped polysilicon deposited by CVD.Generally the thickness of the gate layer 1908 is from about 40-50 Å,and the first and second dielectric layers 1902, 1910, from about 20-80Å.

Referring to FIG. 19B, a first opening 1912 is etched through theoverlying gate layer 1908, and the first and second dielectric layers1902, 1910, to the diffusion region 1904 in the substrate 1906. Next,layers of a tunneling oxide 1914, charge-trapping region 1916, andblocking dielectric 1918 are sequentially deposited in the opening andthe surface of the upper dielectric layer 1910 planarize to yield theintermediate structure shown in FIG. 19C.

Although not shown, it will be understood that as in the embodimentsdescribed above the charge-trapping region 1916 can include a splitcharge-trapping region comprising at least one lower or bottomcharge-trapping layer closer to the tunnel oxide 1914, and an upper ortop charge-trapping layer overlying the bottom charge-trapping layer.Generally, the top charge-trapping layer comprises a silicon-rich,oxygen-lean nitride layer and comprises a majority of a charge trapsdistributed in multiple charge-trapping layers, while the bottomcharge-trapping layer comprises an oxygen-rich nitride or siliconoxynitride, and is oxygen-rich relative to the top charge-trapping layerto reduce the number of charge traps therein. In some embodiments, thesplit charge-trapping region 1916 further includes at least one thin,intermediate or anti-tunneling layer comprising a dielectric, such as anoxide, separating the top charge-trapping layer from the bottomcharge-trapping layer.

Next, a second or channel opening 1920 is anisotropically etched throughtunneling oxide 1914, charge-trapping region 1916, and blockingdielectric 1918, FIG. 19D. Referring to FIG. 19E, a semiconductingmaterial 1922 is deposited in the channel opening to form a verticalchannel 1924 therein. The vertical channel 1924 can include an annularregion in an outer layer of a substantially solid cylinder ofsemiconducting material, or, as shown in FIG. 19E, can include aseparate, layer semiconducting material 1922 surrounding a cylinder ofdielectric filler material 1926.

Referring to FIG. 19F, the surface of the upper dielectric layer 1910 isplanarized and a layer of semiconducting material 1928 including asecond, doped diffusion region 1930, such as a source or a drain, formedtherein deposited over the upper dielectric layer to form the deviceshown.

Referring to FIG. 20A, in a gate last scheme a dielectric layer 2002,such as an oxide, is formed over a sacrificial layer 2004 on a surfaceon a substrate 2006, an opening etched through the dielectric andsacrificial layers and a vertical channel 2008 formed therein. As withembodiments described above, the vertical channel 2008 can include anannular region in an outer layer of a substantially solid cylinder ofsemiconducting material 2010, such as polycrystalline or monocrystallinesilicon, or can include a separate, layer semiconducting materialsurrounding a cylinder of dielectric filler material (not shown). Thedielectric layer 2002 can comprise any suitable dielectric material,such as a silicon oxide, capable of electrically isolating thesubsequently formed gate layer of the memory device 1800 from anoverlying electrically active layer or another memory device. Thesacrificial layer 2004 can comprise any suitable material that can beetched or removed with high selectivity relative to the material of thedielectric layer 2002, substrate 2006 and vertical channel 2008.

Referring to FIG. 20B, a second opening 2012 is etched through theetched through the dielectric and sacrificial layers 2002, 2004, to thesubstrate 1906, and the sacrificial layer 2004 etched or removed. Thesacrificial layer 2004 can comprise any suitable material that can beetched or removed with high selectivity relative to the material of thedielectric layer 2002, substrate 2006 and vertical channel 2008. In oneembodiment the sacrificial layer 2004 comprises that can be removed byBuffered Oxide Etch (BOE etch).

Referring to FIGS. 20C and 20D, layers of a tunneling oxide 2014,charge-trapping region 2016, and blocking dielectric 2018 aresequentially deposited in the opening and the surface of the dielectriclayer 2002 planarize to yield the intermediate structure shown in FIG.20C. In some embodiments, such as that shown in FIG. 20D, thecharge-trapping region 2016 can be a split charge-trapping regionincluding at least a first or inner charge trapping layer 2016 a closestto the tunnel oxide 2014, and a second or outer charge trapping layer2016 b. Optionally, the first and second charge trapping layers can beseparated by an intermediate oxide or anti-tunneling layer 2020.

Next, a gate layer 2022 is deposited into the second opening 2012 andthe surface of the upper dielectric layer 2002 planarized to yield theintermediate structure illustrated in FIG. 20E. As with embodimentsdescribed above, the gate layer 2022 can comprise a metal deposited or adoped polysilicon. Finally, an opening 2024 is etched through the gatelayer 2022 to form control gate of separate memory devices 2026.

Thus, a method for fabricating a nonvolatile charge trap memory devicehas been disclosed. In accordance with an embodiment of the presentinvention, a substrate is subjected to a first radical oxidation processto form a first dielectric layer in a first process chamber of a clustertool. A charge-trapping layer may then be deposited above the firstdielectric layer in a second process chamber of the cluster tool. In oneembodiment, the charge-trapping layer is then subjected to a secondradical oxidation process to form a second dielectric layer above thecharge-trapping layer by oxidizing a portion of the charge-trappinglayer in the first process chamber of the cluster tool. By forming alllayers of an oxide-nitride-oxide (ONO) stack in a cluster tool,interface damage may be reduced between the respective layers. Thus, inaccordance with an embodiment of the present invention, an ONO stack isfabricated in a single pass in a cluster tool in order to preserve apristine interface between the layers in the ONO stack. In a specificembodiment, the cluster tool is a single-wafer cluster tool.

What is claimed is:
 1. A method of fabricating a memory device,comprising: subjecting a substrate to a first oxidation process to forma tunnel oxide layer overlying a channel connecting a source and a drainof the memory device formed in the substrate, wherein the channelcomprises polysilicon; forming a multi-layer charge storing layeroverlying the tunnel oxide layer, the multi-layer charge storing layercomprising an oxygen-rich, first layer comprising a nitride on thetunnel oxide layer in which a stoichiometric composition of the firstlayer results in it being substantially trap free, and an oxygen-lean,second layer comprising a nitride on the first layer in which astoichiometric composition of the second layer results in it being trapdense; and subjecting the substrate to a second oxidation process toconsume a portion of the second layer and form a high-temperature-oxide(HTO) layer overlying the multi-layer charge storing layer.
 2. Themethod of claim 1, wherein the second oxidation process comprises aplasma oxidation process.
 3. The method of claim 2, wherein the channelcomprises recrystallized polysilicon.
 4. The method of claim 1, whereinthe second oxidation process comprises an In-Situ Steam Generation(ISSG) process.
 5. The method of claim 4, wherein the channel comprisesrecrystallized polysilicon.
 6. The method of claim 4, wherein thechannel comprises a silicon nanowire.
 7. The method of claim 1, whereinat least one of the first or second oxidation processes is a radicaloxidation process comprising flowing hydrogen (H₂) and oxygen (O₂) gasinto a process chamber, and forming radicals at a surface of the secondoxynitride layer to consume a portion of the second layer and form theHTO layer without an ignition event to pyrolyze the H₂ and O₂.
 8. Themethod of claim 1, wherein the first layer is separated from the secondlayer by an anti-tunneling layer comprising an oxide.
 9. A method offabricating a memory device, comprising: subjecting a substrate to afirst oxidation process to form a tunnel oxide layer overlying a channelconnecting a source and a drain of the memory device formed in thesubstrate, wherein the channel comprises polysilicon; forming amulti-layer charge storing layer overlying the tunnel oxide layer, themulti-layer charge storing layer comprising a first layer comprising anitride closer to the tunnel oxide layer, and a second layer comprisinga nitride, wherein the first layer is separated from the second layer byan anti-tunneling layer comprising an oxide; and subjecting thesubstrate to a second oxidation process to consume a portion of thesecond layer and form a high-temperature-oxide (HTO) layer overlying themulti-layer charge storing layer.
 10. The method of claim 9, wherein thesecond oxidation process comprises a plasma oxidation process.
 11. Themethod of claim 10, wherein the channel comprises recrystallizedpolysilicon.
 12. The method of claim 9, wherein the second oxidationprocess comprises an In-Situ Steam Generation (ISSG) process.
 13. Themethod of claim 12, wherein the channel comprises recrystallizedpolysilicon.
 14. The method of claim 12, wherein the channel comprises asilicon nanowire.
 15. The method of claim 9, wherein at least one of thefirst or second oxidation processes is a radical oxidation processcomprising flowing hydrogen (H₂) and oxygen (O₂) gas into a processchamber, and forming radicals at a surface of the second oxynitridelayer to consume a portion of the second layer and form the HTO layerwithout an ignition event to pyrolyze the H₂ and O₂.
 16. A method offabricating a memory device, comprising: forming on a surface of asubstrate a stack of layers including at least a first dielectric layer,a gate layer and a second dielectric layer, wherein the gate layer isseparated from the surface of the substrate by the first dielectriclayer and the second dielectric layer is separated from the firstdielectric layer by the gate layer; forming an opening extending throughthe stack of layers to a first doped diffusion region formed on thesurface of the substrate; forming on sidewalls of the opening ahigh-temperature-oxide (HTO) layer; forming on an inside sidewall of theHTO layer a multi-layer charge storing layer, the multi-layer chargestoring layer comprising an oxygen-lean, first oxynitride layer on theHTO layer in which a stoichiometric composition of the first oxynitridelayer results in it being trap dense, and an oxygen-rich, secondoxynitride layer on the first oxynitride layer in which a stoichiometriccomposition of the first oxynitride layer results in it beingsubstantially trap free; forming on an inside sidewall of themulti-layer charge storing layer a tunnel oxide layer; and forming on aninside sidewall of the tunnel oxide layer a vertical channel comprisingpolysilicon, wherein the vertical channel electrically couples firstdoped diffusion region to a second doped diffusion region formed in alayer of semiconducting material subsequently formed over the stack oflayers and the opening.
 17. The method of claim 16, wherein the HTOlayer is formed by a plasma oxidation process.
 18. The method of claim16, wherein the HTO layer is formed by an In-Situ Steam Generation(ISSG) process.
 19. The method of claim 16, wherein the first oxynitridelayer is separated from the second oxynitride layer by an anti-tunnelinglayer comprising an oxide, and wherein the HTO layer is formed by aplasma oxidation process.
 20. The method of claim 16, wherein the firstoxynitride layer is separated from the second oxynitride layer by ananti-tunneling layer comprising an oxide, and wherein the HTO layer isformed by an In-Situ Steam Generation (ISSG) process.